1. FIELD OF THE INVENTION
This invention relates to a method for making an article such as a chair seat or the like in a closed cavity by expansion of a polymerizing material.
2. DESCRIPTION OF THE PRIOR ART
Many attempts have been made to produce chair seats and other such structural articles from rigid plastic materials, such as cured, rigid foams. Materials that have been found to be useful for such an approach include polyolefin foams polystyrene foams, polyester foams, polypropylene foams, and polyurethane foams. Many different methods exist for producing articles in this type of operation. Generally, when the production is such that the amount of plastic material or foam material that is used is of a large quantity, a portion of the material is replaced by some type of rigid insert which is of a lower cost, but which still provides sufficient rigidity to prevent a weakening of the article produced. Generally, such production is of the type wherein the rigid material is inserted into one-half of the mold and the foamable material is inserted into the other half, with the two halves then being placed together in order that the foamable material may expand as it cures and foam upward and around the rigid material to form a single unitary piece of rigid hard structure. Several methods exist for obtaining this goal. In U.S. Pat. No. 3,608,007, a rigid desk top or the like is produced by using a resin impregnated paper as a hard outer shell with the paper shell then filled with a polyurethane foam that is then cured to provide a solid structure. With this method, however, the gas that is formed in the reaction is retained within the structure causing it to expand, and although the structure is rigid and hard, it nevertheless has a large amount of expansion due to gases retained therein. This expansion weakens the structural strength of the article produced. In U.S. Pat. No. 3,531,552, a seat is produced with a foam cushion having a rigid insert therein for support, but ample space is provided within the cavity itself for expansion of the material, and the insert is of a nature that will allow for it to absorb the foaming gases to render the foam free of voids. Both of these processes thus make provisions within the mold cavity itself for retention of the foaming gases within the cavity. One other known method for making an integral formed seat, illustrated in U.S. Pat. No. 3,845,183, includes a process for making a seat having a rigid insert therein, although the foam material is eventually a soft material with an integral skin in order to have resiliency. In this method, the cavity is entirely closed and flashing chamber within the cavity allows for expansion of the foam material due to the generated gases. The continuous flash formed in the expansion portion of the chamber is then severed and discarded. In each of these methods, some provision within the chamber itself is made for accommodating the reaction gases within the chamber.
Perhaps the closest thing to the present invention is the teaching in U.S. Pat. No. 3,844,523. In that patent, an air permeable material is simply placed between two mold halves. In that process, however, the air permeable material must be sufficiently rigid to keep from distorting into the mold cavity thereby causing a design imperfection in the cast article. That process, however, is undesirable for certain systems since to have a material of sufficient rigidity to extend across a large cavity requires a material of reduced gas permeability. In the present invention, the lack of rigidity over large cavity expanses is overcome by a rigid insert which is attached to the air permeable material to additionally support it and with the rigid insert thereafter becoming an integral part of the molded article.
The new and novel method of this invention provides a system for removal of the expansion gases from the mold cavity without allowing the polymer material to expand out of the mold cavity thus providing a rigid system, hard and solid throughout, which has the strength and appearance of hardwood.